Russian authorities on Thursday closed all four of Moscow's airports, plus a fifth one in a city about 100 miles southwest of the country's capital, citing unspecified safety concerns.

All four of Moscow's airports including another about 100 miles southwest of the Russian capital were temporarily shut down for undisclosed security concerns, authorities said.

Russia's aviation watchdog said on Thursday all four Moscow airports had resumed work after the lifting of temporary restrictions that were introduced to ensure the safety of civil aircraft flights. "Aircraft crews,